1. Field of the Invention
The present invention relates to an actuator and an exhaust brake unit using the actuator, especially the actuator whose power rod performs a rotary motion and the exhaust brake unit to control exhaust gas control valve such as a butterfly type valve body provided in an exhaust channel of motor vehicle, using the actuator.
2. Description of the Related Art
A diaphragm actuator is well known as a conventional actuator. A standard diaphragm actuator has an upper cover with a negative or positive pressure inlet, a lower cover fixed to the upper cover, a diaphragm installed between the upper cover and the lower cover and is constituted to present an output of the motion of the diaphragm induced through the introduction of negative pressure to the outside mechanisms.
The exhaust brake unit is mounted mainly on trucks or buses and used as an auxiliary brake to counteract the acceleration of vehicles that are descending a hill by closing an exhaust gas control valve arranged at some midpoint on an exhaust pipe.
In the exhaust brake unit, the actuator is used to actuate the exhaust gas control valve arranged in some midpoint on the exhaust pipe in a way that output from a power rod of the actuator is transmitted to the exhaust gas control valve through a link system.
In other words, a linear motion of the power rod of the actuator is converted to rotary motion through the link system to perform an open/close operation of the exhaust gas control valve.
Further, the conventional technique will be explained in detail using FIG. 11 showing an actuator and an exhaust brake unit using the invention disclosed in the bulletin of Japanese Patent Application Laid-open No. Hei 5-171961. FIG. 11 shows a sectional view of an exhaust gas control valve and an actuator.
As shown in the figure, an exhaust channel 101 is formed in a body 100 of the exhaust gas control valve, shaft holes 103 to insert through a valve shaft 102 are bored on both side wall portions, a butterfly type valve body 104 is arranged in the exhaust channel 101 in a way that the butterfly type valve body 104 opens and closes the exhaust channel 101, and the valve body 104 is fixed to the valve shaft 102 with bolts. The right side portion of the valve shaft 102 is extended to connect to the actuator. And the valve shaft 102 is inserted through the shaft hole 103 on the body 100, a bush 105 is slid on the valve shaft in the left shaft hole 103, and the other end of the shaft hole 103 is closed with a closing plate 106.
A seal ring 107 is put on the outer periphery of the valve shaft 102 in the right shaft hole, a bush 108 is inserted on the right of the seal ring 107. The top of the valve shaft 102 protrudes from the body 100, a plate 109 is tightened with screws on the side portion of the body 100 to seal the shaft hole 103. A power rod 112 of a diaphragm actuator 111 is connected to the valve shaft 102 protruding from the body 100 through a link lever 110. The diaphragm actuator 111 is fixed to the body 100 through a bracket 113.
The actuator 111 has on the inside a first room 115a and a second room 115b divided by a diaphragm 114 and a negative pressure inlet 117 is arranged at the side of the first room 115a. The power rod 112 is connected to the central portion of the diaphragm 114 through a retainer 116, and an end portion of the power rod 112 is connected to the valve shaft 102 through the link lever 110. A spring 118 is provided in the second room to return the retainer 116 to the original state.
In the exhaust brake unit thus structured, the exhaust gas control valve is usually conditioned to open the exhaust channel 101.
A switch for the exhaust brake is turned on in a driving state of the engine and when a driver's feet are away from the accelerator pedal and the clutch pedal, the diaphragm 114 and the retainer 116 are moved by the introduction of the negative pressure from a vacuum tank installed on the vehicle in the first room 115a and the power rod 112 gets to move in a linear motion. The motion is converted to rotary motion through the link lever 110 so that the valve body 104 closes the exhaust channel 101.
As a power rod of the conventional actuator is connected to a diaphragm, it moves in a linear motion. Accordingly, in order to operate an exhaust gas control valve such as a butterfly type valve body with the power rod, a link system to convert a linear motion to a rotary motion is essential.
However, as the conventional link system is installed on the outside of an actuator and uses a long lever, a technical problem is an increase in size of the whole exhaust brake unit and the necessity of a large space for the installation into a vehicle.
Especially, when an actuator is vertically installed as shown in FIG. 11, the height of the exhaust brake unit is increased and makes it difficult to install into a vehicle. To solve the problem, there is a case that the actuator is installed in a body so that the actuator is placed parallel to the exhaust channel (the power rod is placed parallel to the exhaust channel).
In this exhaust brake unit, the height can be lowered, but another technical problem is that a heat shield plate becomes necessary between the actuator and the body having the exhaust channel, because the actuator is located near the exhaust channel.
And when the actuator is installed at the place of the power rod intersecting the shaft line of the valve shaft, the linear motion of the power rod is disturbed by the valve shaft so that the linear motion can not be converted to rotary motion. To avoid the problem, the actuator must be so placed that the axis of the power rod does not coincide with the axis of the valve shaft. Another technical problem is the increase in size of the exhaust brake unit.
In the conventional exhaust brake unit, as the linear motion of the power rod is converted to rotary motion of the exhaust gas control valve, the actuator must be so placed that the axis of the power rod be on a surface perpendicular to the shaft line of the valve. Then, the requirement that the actuator is arranged in the shaft line of the valve (actuator is so placed that the axis of the power rod of the actuator is on the same straight line with the shaft line of the valve) can not be satisfied. This limitation in designing a vehicle is yet another technical problem.
Further, when the actuator is assembled with the exhaust gas control valve, the link system must be fitted to the valve shaft and the rod. Thus assembling is not easy.
An object of the present invention is aimed to solve the above described technical problems and to provide an actuator which is able to output the power as rotary motion from the output of the rod of the actuator.
And it is also an object of the present invention to provide an exhaust brake unit which using the actuator, is easy to assemble, requires a small space to install, able to arrange the actuator so that the axis of the power rod and the shaft line of the valve are on the same straight line, and minimizes heat transmission from the exhaust channel to the actuator.